The CENTRAL HYPOTHESIS of this grant application is that co-stimulatory blockade will effectively enhance human islet allograft survival in patients with Type 1 diabetes and, when combined with additional immunomodulatory strategies, will result in donor specific tolerance and prevention of reoccurrence of autoimmune beta cell destruction. The proposed immunomodulatory approaches will include recipient treatment with humanized anti-CD154, anti-B7.1/B7.2, and anti-CD45RB specific monoclonal antibodies. Infusion of stem cell (CD34 selected) enriched fractions, obtained from the islet donors' vertebral bodies, will also be tested in the presence of costimulatory blockade. They hypothesize that these multifaceted strategies will promote graft survival in the short term via the induction of anergy and/or clonal deletion and result in donor specific tolerance over the long term. They have strong preliminary results in non-human primate (NHP) models demonstrating that co-stimulatory blockade via antiCD154 monotherapy allows for engraftment and long term insulin independence and preservation of functional islet mass. Several monkeys treated with anti-CD154 for a period of 6 months to one year are maintaining islet and renal allograft function after discontinuation of therapy, with no evidence of rejection. The recent availability of this powerful immunointervention agent provides a unique opportunity to explore the tolerogenic potential of costimulatory blockade and other immunomodulatory strategies on human islet allograft survival in selected pilot trials, aimed at identification of clinically relevant tolerogenic protocols. To better accomplish the goals of this RFA, and in line with our overall institutional mission, we have successfully established a network of collaborations and partnerships with key institutions, including the NIDDK/Navy, Harvard, Yale, Stanford, the University of Giessen, the University of Alabama and the University of Florida. They propose the following specific aims: Specific Aim #1: To define the best immunomodulatory strategy that will allow for permanent islet allograft survival, donor specific unresponsiveness in the absence of chronic recipient immunosuppression and prevention of recurrent beta cell autoimmune destruction. Specific Aim #2: To assess metabolic function of successful intrahepatic islet allografts. Specific Aim #3: To study immune alterations that lead to tolerance in islet allograft recipients.